1. Field of the Invention
The present invention relates to an aluminum nitride sintered body, a semiconductor manufacturing member, and a method of manufacturing the aluminum nitride sintered body.
2. Description of the Related Art
Heretofore, in semiconductor manufacturing processes and liquid crystal manufacturing processes, an electrostatic chuck is used which clamps and holds a semiconductor substrate or a glass substrate. Electrostatic chucks include one which clamps a substrate using a Coulomb force and one which clamps a substrate using a Johnson-Rahbek force. The Coulomb force is an electrostatic clamping force generated between a substrate mounted on a surface of a dielectric material layer of the electrostatic chuck and an electrode of the electrostatic chuck. In the electrostatic chuck, high volume resistance is needed in order to obtain an electrostatic force for clamping the substrate. For example, in the electrostatic chuck using the Coulomb force, alumina, which is a material having a high volume resistivity, is used as a material for a base plate.
However, general alumina sintered bodies have thermal conductivities as low as approximately 20 W/mK. Very-high-purity, high-thermal-conductivity ones have thermal conductivities of approximately 30 W/mK. Even single crystal ones have thermal conductivities of approximately 40 W/mK and cannot sufficiently satisfy thermal conductivities required for, for example, electrostatic chucks.
Accordingly, aluminum nitride, which is a material having high volume resistance while satisfying thermal conductivity, is being used as the material for the base plate (e.g., Japanese Patent Laid-open Publication No. 2002-220282).
However, recently, aluminum nitride sintered bodies used in semiconductor manufacturing equipment tend to be increasingly exposed to high-temperature environments. For example, base temperature ranges are becoming wide in etching processes, high-density plasma CVD, and the like. With this, the material is desired, which maintains the high volume resistivity even in high-temperature environments.
Furthermore, in the electrostatic chuck using the Coulomb force, a high voltage is applied to the base plate in order to generate the Coulomb force. Accordingly, the material is desired which maintains the high volume resistivity even in high-voltage environments.
If no particular innovation is made, the aluminum nitride sintered body generally has a volume resistivity of not less than 1×1015 Ωcm during voltage application of 500 V/mm at room temperature, thus having high volume resistance. However, for example, in a temperature region of 200° C., which is an operating environment, in the case of voltage application of 2 kV/mm, the volume resistivity is not more than 1×1014 Ωcm. Thus, there is a problem that the volume resistivity decreases in the high-temperature, high-voltage environment. According to this, for example, when the aluminum nitride sintered body is used as the electrostatic chuck, electric charges remain on the surface of the electrostatic chuck even after voltage application is stopped, and the substrate is not immediately detached therefrom. Thus, there is apprehension that responding characteristics in attachment and detachment may be considerably affected.